The present invention relates to a crude oil processing apparatus for separating water from crude oil, and a crude oil processing method.
This application is based on Japanese Patent Applications (Japanese Patent Application No. Hei 10-48303and Japanese Patent Application No. Hei 10-48306) filed in Japan, the contents of which are incorporated herein as a part of this specification.
Crude oil contains as principal components paraffin, naphthene, aromatic and other hydrocarbons. The physical and chemical properties of the crude oil are determined by the proportion of various chemical compounds contained therein, and the properties of the crude also vary significantly from oil field to oil field, and from horizon to horizon.
It is an internationally accepted practice to represent the specific gravity of crude oil with API (American Petroleum Institute) gravity. API gravity is determined as follows.
API gravity=(141.5/G)xe2x88x92131.5 
where G is the ratio of the mass of crude oil at 60xc2x0 F.(15.6xc2x0 C.) to the mass of water of the same volume at 60xc2x0 F. Various types of crude oil are roughly classified as follows in terms of API gravity.
Crude oil is produced by, first, collecting the crude oil from various oil reservoirs in the ground through oil wells by flowing, pumping, water or gas injection, or other methods. The crude oil that has been collected is sent from a branch pipe, called the Christmas tree which is installed on the well head, through a pipeline embedded underground to an oil gathering station. The crude oil gathered at the oil gathering station is sent to a separator where gas and water are separated from the crude oil.
FIG. 8 shows an example of the separator. Separators are roughly classified into horizontal, vertical and spherical types. The example shown is of the horizontal type.
The separator 201 of the example comprises a closed tank that has a crude oil inlet 202 provided at a position a little above the center of the side wall on one end, a separated oil outlet 213 provided at a position a little below the center of the side wall on the other end, a separated water outlet 212 provided at the bottom on the other end, and a gas outlet 214 installed at the top. Provided in the separator 201 are a weir plate 203 installed near the crude oil inlet 202 to suppress billowing of the crude oil that has been introduced, and a partition wall 215 installed on the other end to allow only the supernatant (separated oil) of the liquid in the crude oil layer 204 to overflow into the separated oil layer 206 on the separated oil outlet 213 side.
To remove water from the crude oil using the separator 201 having such a constitution as described above, first, the crude oil sent from the production well is introduced rapidly through the crude oil inlet 202 into the separator 201. After billowing has been quelled near the crude oil inlet 202, the crude oil passes the weir plate 203 and into the crude oil layer 204 of the next section.
Gas that has escaped from the crude oil layer 204 is accumulated in a gas layer 205 located above in the separator 201, and is occasionally discharged through a gas outlet 214. The crude oil layer 204 separates over time into oil and water due to differences in specific gravity, and water is accumulated into a separate lower water layer 207. The crude oil is heated to a temperature in a range from 40 to 60xc2x0 C., thereby decreasing the viscosity of the crude oil, to improve the efficiency of separation. Water in the separated water layer 207 is occasionally discharged through a separated water outlet 212 by opening and closing a water level control valve 210 under the control of a water level controller 208. The separated oil that is free of gas and water by separating from the crude oil layer 204 flows over the partition wall 215 into a separated oil layer 206. The separated oil in the separated oil layer 206 is occasionally discharged through a separated oil outlet 213 by opening and closing an oil level control valve 211 under the control of an oil level controller 209.
The method of separating water from the crude oil by making use of differences in specific gravity between oil and water using the separator 201 described above requires an increase in the scale of the facilities when the quantity of crude oil to be processed is increased, thus giving rise to such problems as the selection of site to build the facility, equipment investment cost for the facility and energy cost of the heating boiler. Moreover, such problems as the limitations to the processing rate and capacity and limitations to reduction of the water content make it difficult to increase the processing capacity by increasing the scale of the facility.
In the meantime, the separated oil from which gas and water are removed may still include a significant water content, with fine water particles and muddy matter uniformly dispersed therein depending on the nature of the crude oil. Such a dispersed state is called an emulsion. Such fine water particles would not be caused to aggregate into separable water simply by leaving the oil to stand still. This is because the surface tension of the fine water particles is strong and hinders the water particles from combining.
Also the muddy matter can corrode the processing facility after separation. The muddy matter may also have a composition that is not suited to refining and production, in which case that production yield may become lower.
Thus in order to decrease the water content in the separated oil, processes such as the following are employed: (1) to destroy the adsorption membrane of the water particles by using a surfactant thereby to cause the water particles in the emulsion to aggregate into separable water; and (2) to apply a high AC voltage of 10 kV to 20 kV to make an AC current flow through the emulsion thereby to reorient the adsorption membrane of the water particles under the effect of the electric field into such a state that the water particles collide with each other more frequently and also attract each other, thereby causing the water particles in the state of emulsion to aggregate into separable water.
However, the process (1) of adding the surfactant requires the choice of the surfactant best suited for the oil temperature, oil processing rate, components of the oil and the concentration of salt content in the oil, and makes it necessary to determine the surfactant adding condition. Also there has been the problem that the surfactant is subject to a strong limitation due to the concentration of salt content in the oil or water, and therefore the conditions of use must be studied and determined according to which location and horizon of the oil field the crude oil comes from.
Also the process (2) of applying a high AC voltage has the problems of the site to build the facility, equipment investment and cost of the facility, the possibility of fire caused by the high voltage, fire prevention measures and the method of supplying electric power.
Among the different types of crude oil described previously, bitumen and heavy oil have particularly high values of specific gravity, close to that of water, and therefore take a longer time to separate from water.
The first embodiment of the present invention provides a crude oil processing apparatus for separating and removing water contained in crude oil, comprising a processing tank having a water drainage port at the bottom, a membrane that selectively allows the oil content of the crude oil to pass therethrough installed in the processing tank, a means which pressurizes the crude oil and a removal pipe for removing dehydrated oil that has passed the membrane.
The first embodiment of the present invention also provides a crude oil processing method, which comprises immersing a membrane module in crude oil contained in a processing tank, pressurizing the crude oil to pass through the membrane, and removing the dehydrated oil that has passed therethrough through an oil collecting pipe.
According to the first embodiment, a high degree of separation and removal of water from the crude oil can be accomplished regardless of the properties of the crude oil, and muddy matter can also be separated and removed. As a result, dehydrated oil having a lower water content and no muddy matter contained therein can be obtained without using a surfactant or applying a high voltage. Pressurizing the crude oil against the membrane also makes it possible to process the crude oil efficiently without waiting for the water content to precipitate due to the difference in the specific gravity as in the prior art. Consequently, it is possible to process a large quantity of crude oil in a small apparatus.
The second embodiment of the present invention provides a crude oil processing apparatus for separating and removing water contained in crude oil, comprising a processing tank having a water drainage port at the bottom, a membrane that selectively allows the oil content of the crude oil to pass therethrough installed in the processing tank, and a removal pipe one end of which communicates with a passage of dehydrated oil that has passed the membrane and opens on the other end thereof at a position lower than the crude oil surface in the processing tank.
The second embodiment of the present invention also provides a crude oil processing method, which comprises immersing a membrane module in crude oil contained in a processing tank, conducting gravitational filtration to make the crude oil pass through said membrane, and removing the dehydrated oil obtained in the gravitational filtration through an oil collecting pipe.
According to the second embodiment, since a level difference is provided between the surface of the crude oil in the processing tank and the position where the dehydrated oil removal pipe opens, thereby to carry out gravitational filtration of the crude oil through the membrane by the use of a pressure difference due to gravitational force, the oil-water separation process of the crude oil by means of the membrane can be accomplished without applying a driving force from the outside to the membrane. Thus, a high degree of separation and removal of water from the crude oil can be accomplished regardless of the properties of the crude oil, and muddy matter can also be separated and removed. As a result, dehydrated oil having a lower water content and no muddy matter contained therein can be obtained without using the surfactant or applying a high voltage.